The present invention relates to identification codes, formation methods for identification codes, liquid droplet ejection apparatuses, and electro-optic apparatuses.
Normally, an electro-optic apparatus such as a liquid crystal display and an organic electroluminescence display (an organic EL display) includes a transparent glass substrate (hereinafter, a “substrate”) for displaying an image. The substrate has an identification code (for example, a two-dimensional code), which represents product information including a manufacturer and a product number, for purposes of quality control and production control. The identification code includes a plurality of dots defined by, for example, colored thin films or recesses. The dots are arranged in such a manner as to form a predetermined pattern. The identification code is determined in correspondence with the arrangement pattern of the dots.
As a method for forming the identification code, Japanese Laid-Open Patent Publication No. 11-77340 discloses a laser sputtering method and Japanese Laid-Open Patent Publication No. 2003-127537 discloses a waterjet method. In the laser sputtering method, dots are deposited through sputtering by radiating a laser beam onto a metal foil. In the waterjet method, dots are marked by ejecting water containing abrasive onto a substrate.
However, in the laser sputtering method, the space between the metal foil and the substrate must be adjusted to several micrometers to several tens of micrometers in order to form each dot to a desired size. The substrate and the metal foil thus must have surfaces that are reliably formed flat. Further, adjustment of the space between the substrate and the metal foil must be carried out with high accuracy in the order of micrometers. This limits application of the method to a restricted range of substrates, and the use of the method is limited. In the waterjet method, the substrate may be contaminated by the water, dust, and the abrasive that are splashed when the identification code is formed.
In order to solve these problems, an inkjet method has been focused on recently. In the inkjet method, dots are provided by ejecting microdroplets of liquid containing metal particles onto the substrate by a liquid droplet ejection apparatus. The microdroplets are then dried and thus corresponding dots are formed. The method thus can be applied to a relatively wide range of substrates. Further, the method prevents contamination of the substrate when forming the identification code.
However, the dots formed by the inkjet method have relatively low bonding strength with the substrate and thus easily separate from the substrate. Thus, if the identification code contacts and scrapes against, for example, a surface of a transport stage, the dots may be peeled off from the substrate and thus cause loss of the product information marked on the substrate.